A local area network (LAN) or a similar computing network typically consists of one or more server computers connected through conductive cabling to one or more client computers. FIG. 1 illustrates a portion 5 of such a network. A hub 10, a router, or a similar device is coupled through cable 150 to a desktop computer 20 or a similar device. The cable 150 might include lengths of twisted pair cables, patch cords, and other standard conducting cables. The hub 10 is coupled to the cable 150 by a first connector 130 and the computer 20 is coupled to the cable 150 by a second connector 140.
Testing can be done to verify the integrity of the cable 150 by replacing the hub 10 and the computer 20 with test devices, as shown in FIG. 2. A first test device 110 transmits a test signal through the cable 150 to a second test device 120. The test signal is typically a radio frequency signal that is varied between a lower frequency and a higher frequency. The second test device 120 receives the test signal response and analyzes it to determine cable gain or far-end crosstalk at each frequency. Cable gain (insertion gain) is always less than one because the cable always exhibits loss. In some cases, the test signal is returned through the cable 150 to the first test device 110, which then performs the analysis.
The test equipment may be based on a pulse response, where the system is excited by a pulse and the time domain of the system is then converted to the frequency domain by use of Fourier transforms to obtain the frequency response of the system.
The test device 110 or 120 performing the analysis can measure several different parameters such as Return Loss and near-end crosstalk (NEXT). Return Loss is expressed as the ratio of the transmitted signal power to the reflected signal power and is usually expressed in dB. NEXT is the ratio of the transmitted signal power on one channel to the received crosstalk power on another channel at the same location (i.e., the same end of the cable) and is usually expressed in dB. Other parameters that might be examined include attenuation and equal level far-end crosstalk.
The connectors 130 and 140 can cause Return Loss, NEXT, and other effects by introducing capacitance, inductance, or both into the test signal response. When both capacitance and inductance are present and physically located together, they can be combined into a single point source equivalent reactance, which may be capacitive or inductive. The connectors 130 and 140 and other point sources of reactance that might be present in the cable 150 can be referred to as reactive point source disturbances (RPSDs).
Various organizations publish standards and guidelines describing how LAN testing should be conducted. These guidelines typically require that only the portion of the cable 150 known as the channel 155, which runs between but does not include connectors 130 and 140, should be analyzed. That is, the effects of the connectors 130 and 140 are not to be included in the analysis of the test signal response. This can complicate the test procedures because the test signal must pass through the connectors 130 and 140. Any reactance introduced by the connectors 130 and 140 must be accounted for in the analysis of the test signal response.